This invention relates generally to a liquid crystal display. More particularly, the present invention relates to a driving signal generator for a liquid crystal display.
Generally, a twisted nematic mode liquid crystal display (LCD), which uses thin film transistors (TFTs) as switching elements, is supplied with an analog voltage of 5V as a liquid crystal driving voltage.
Recently, however, as the resolution of TFT LCDs has increased, the number of pixels in a display has similarly increased. This brings rise to the problem of electromagnetic interference (EMI) occurring in high resolution LCDs. In particular, EMI occurs in these high resolution LCDs in a digital circuit section such as a drive integrated circuit, since the relatively high voltages are used to drive the digital circuit.
Accordingly, to overcome this problem in high resolution TFT LCD modules, a lower voltage (about 3.3V) has been used to drive the digital circuit section. As a result, this means that the TFT LCD required both an analog voltage (5V) for driving the liquid crystal and a lower digital voltage (3.3V) for driving the digital circuit.
FIGS. 1 and 2 are detailed schematic diagrams of conventional circuits for generating the analog voltage (5V) and the digital voltage (3.3V) in the TFT LCD when the supplied power voltage V.sub.cc is 5V and 3V, respectively.
As shown in FIG. 1, when a supplied power voltage V.sub.CC is 5V, the digital voltage V.sub.o of 3.3V is obtained by a voltage drop using an npn-type bipolar transistor Q.sub.1 while the analog voltage V.sub.a of 5V is obtained by a DC/DC converter 10.
As shown in FIG. 2, when the supplied power voltage V.sub.CC is 3.3V, the digital voltage V.sub.o of 3.3V is obtained directly while the analog voltage V.sub.a of 5V is generated by the DC/DC converter 10.
There is a problem in the conventional circuits, however, in that the productivity of the TFT LCD module decreases since different voltage generation boards are required depending upon the magnitude of the supplied driving voltage.